The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

/pdf/planetary-boundaries-guiding-human-development-on-a-changing-5gmf909etg.pdf

Planetary boundaries: Guiding human development on a changing planet

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

/pdf/climate-change-2007-the-physical-science-basis-1x93ttz9jt.pdf

Climate Change 2007: The Physical Science Basis.

[1] EGM2008 is a spherical harmonic model of the Earth's gravitational potential, developed by a least squares combination of the ITG-GRACE03S gravitational model and its associated error covariance matrix, with the gravitational information obtained from a global set of area-mean free-air gravity anomalies defined on a 5 arc-minute equiangular grid This grid was formed by merging terrestrial, altimetry-derived, and airborne gravity data Over areas where only lower resolution gravity data were available, their spectral content was supplemented with gravitational information implied by the topography EGM2008 is complete to degree and order 2159, and contains additional coefficients up to degree 2190 and order 2159 Over areas covered with high quality gravity data, the discrepancies between EGM2008 geoid undulations and independent GPS/Leveling values are on the order of ±5 to ±10 cm EGM2008 vertical deflections over USA and Australia are within ±11 to ±13 arc-seconds of independent astrogeodetic values These results indicate that EGM2008 performs comparably with contemporary detailed regional geoid models EGM2008 performs equally well with other GRACE-based gravitational models in orbit computations Over EGM96, EGM2008 represents improvement by a factor of six in resolution, and by factors of three to six in accuracy, depending on gravitational quantity and geographic area EGM2008 represents a milestone and a new paradigm in global gravity field modeling, by demonstrating for the first time ever, that given accurate and detailed gravimetric data, asingle global model may satisfy the requirements of a very wide range of applications

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2011JB008916

The development and evaluation of the Earth Gravitational Model 2008 (EGM2008)

This chapter addresses changes in weather and climate events relevant to extreme impacts and disasters. An extreme (weather or climate) event is generally defined as the occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends (‘tails’) of the range of observed values of the variable. Some climate extremes (e.g., droughts, floods) may be the result of an accumulation of weather or climate events that are, individually, not extreme themselves (though their accumulation is extreme). As well, weather or climate events, even if not extreme in a statistical sense, can still lead to extreme conditions or impacts, either by crossing a critical threshold in a social, ecological, or physical system, or by occurring simultaneously with other events. A weather system such as a tropical cyclone can have an extreme impact, depending on where and when it approaches landfall, even if the specific cyclone is not extreme relative to other tropical cyclones. Conversely, not all extremes necessarily lead to serious impacts. [3.1] Many weather and climate extremes are the result of natural climate variability (including phenomena such as El Nino), and natural decadal or multi-decadal variations in the climate provide the backdrop for anthropogenic climate changes. Even if there were no anthropogenic changes in climate, a wide variety of natural weather and climate extremes would still occur. [3.1] A changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of weather and climate extremes, and can result in unprecedented extremes. Changes in extremes can also be directly related to changes in mean climate, because mean future conditions in some variables are projected to lie within the tails of present-day conditions. Nevertheless, changes in extremes of a climate or weather variable are not always related in a simple way to changes in the mean of the same variable, and in some cases can be of opposite sign to a change in the mean of the variable. Changes in phenomena such as the El Nino-Southern Oscillation or monsoons could affect the frequency and intensity of extremes in several regions simultaneously.

/pdf/changes-in-climate-extremes-and-their-impacts-on-the-natural-1fikyoq21o.pdf

Changes in climate extremes and their impacts on the natural physical environment.

Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6-9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics-including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs-that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.

Contribution of Antarctica to past and future sea-level rise

Geodetic Measurements and Analysis of Glacier Kinematics in East Greenland

This work presents the first results of a research activity aiming to compare estimates of Surface Elevation Changes (SEC) over the Jakobshavn Isbrae basin (Greenland) using different repeat altimetry techniques and different sensors (laser vs. radar altimetry). The goal of this comparison is the identification of the best performing algorithm, in terms of accuracy, coverage and processing effort, for the generation of surface elevation change maps. The methods investigated here are the cross-over and repeat-track. The results of the inter-comparison are here reported and, from a first analysis, it is found that both radar and laser altimetry resolve the surface elevation changes quite well, and that the problems found mainly in the coastal region and along the main trunk can be solved by combining the two methods. The comparison with airborne lidar data from the NASA ICEBridge and the ESA CryoVex campaigns is in progress.

Preliminary results of the ice_sheet_CCI round robin activity on the estimation of surface elevation changes

The Greenland ice sheet is losing mass to the ocean at an increasing rate (Thomas et al. 2006). During the 1980s the ice sheet was believed to be in near-equilibrium (van den Broeke et al. 2009). Within the first decade of the 21st century, however, a net negative balance was observed. Greenland’s present rate of ice loss is c. 250 Gt yr–1, equivalent to a sea-level rise contribution of c. 0.69 mm yr–1. The rate of ice loss has increased over the post 1992 observation period (Shepherd et al. 2012). The ice-sheet mass budget can be partitioned into two main components: (1) surface mass balance (SMB; the net difference between accumulation and surface ablation) and (2) marine ice loss (D; iceberg discharge via glacier dynamics plus subsurface melt at the glacier terminus). Over the past decade, the surface mass-balance proportion has accelerated relative to the D component, changing from c. 50% in 2000–2008 (van den Broeke et al. 2009) to more than two thirds (68%) in 2009–2012 (Enderlin et al. 2014). Whereas modern climate models appear to capture the surface mass-balance response to climate change, the physical processes driving variability in glacier discharge are more complex. Recent increases in D may be due to: (1) changing force-balance at the ice-ocean interface as suggested by model simulations (e.g. Nick et al. 2009, 2013), (2) changing basal lubrication at the ice-bed interface due to increased meltwater availability (Zwally et al. 2002; Andersen et al. 2010), and/or (3) decreasing ice viscosity due to increasing ice temperature (van der Veen et al. 2011). The high spatial variability in these forcing mechanisms and a large sensitivity to local fjord geometry (Nick et al. 2013) require basin scale studies of glacier dynamics to elucidate local causes of glacier acceleration. In 2007 the Programme for Monitoring the Greenland Ice Sheet (PROMICE) was initiated to gain insight into the changing mass balance of the Greenland ice sheet using quantitative meteorological observations, as well as airborne surveys of ice thickness and flow-velocity observations (Ahlstrom et al. 2008). Here we present the first calculations of ice discharge using PROMICE observations, with focus on a West Greenland ice-sheet drainage basin previously defined as ‘Basin 7’ (Zwally et al. 2012; Fig. 1). The c. 400 km long ice-sheet margin within Basin 7 includes the 6 km wide Jakobshavn Isbrae, and several other marine-terminating outlet glaciers, such as Store Gletscher and Rink Isbrae (Figs 1, 2). We combine satellite-derived, ice-surface velocities, airborne ice-thickness measurements, and modelled surface mass balance to assess the dynamic discharge from Basin 7.

/pdf/mass-loss-from-an-ice-sheet-drainage-basin-in-west-greenland-rpsal5mjr2.pdf

Mass loss from an ice-sheet drainage basin in West Greenland

BOOK © E SA 2 01 8 24–29 September 2018 | Ponta Delgada, São Miguel Island Azores Archipelago, Portugal → 25 YEARS OF PROGRESS IN RADAR

/pdf/25-year-time-series-of-multiple-satellite-ice-sheet-changes-22dn45cx3t.pdf

25 Year Time Series of Multiple-Satellite Ice Sheet Changes: the ESA Climate Change Initiative

A New Aerogeophysical Study of the Eurasia Basin and Lomonosov Ridge: Implications for Basin Development

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